Tian Bing

Effect of load on zero-sequence current in low resistance grounding system with complex grounding fault

The events that a single-line fault evolves into a multi-line fault are increasing recently in China Southern Power Grid. To make matters worse, zero-sequence current is closely related to the load in fault lines particularly when a complex multi-line single-phase grounding fault (SPGF) occurs in a low resistance grounding system. In this case, the load factor must be considered, otherwise it may result in unneglectable calculation errors. Therefore, a comprehensive theory analysis on the relation between zero-sequence current and load was carried out for complex multi-line SPGF firstly. On this basis, the influence mechanism of load variation on zerosequence currents was analyzed in detail, and some general rules were revealed at last. The conclusions summarized in this paper can provide a theoretical basis for improving the performance of zero-sequence current protection.

Analysis of overvoltage caused by intermittent earth fault and its suppression method

Intermittent earth faults occur frequently in urban distribution networks, causing overvoltage in the whole system. This paper first presents the distribution characteristics of transient overvoltage caused by intermittent earth faults. Overvoltage level at the end of a sound line turns to be higher than that of the faulted line. In resonant grounding system with Petersen coil based on thyristor controlled reactor (TCR), overvoltage appears to be more severe due to response delay of compensation. Therefore, the influence on overvoltage level of Petersen coil compensation is analyzed, based on which, an overvoltage suppression method is proposed.